Koi fish are a breed of carp that are native to Japan. They are a popular choice of pet all over the world, with millions of people collecting them for their natural beauty.
Koi fish look stunning as they swim through ponds and streams, and some people even believe they bring good fortune.
Given how popular they are as pets, one might assume that koi are completely harmless. Is this really the case?
Or is there more that we need to understand about these beautiful fish? This article will aim to answer the question ‘Are koi fish dangerous to humans?’
Are Koi Fish Aggressive/Dangerous?
It’s very rare for koi fish to act hostile, but this can also depend on their size or weight.
Koi fish are generally known to be passive creatures; they are more likely to swim away than attack when threatened.
However, experienced koi fish keepers know that they should still handle each fish with care, just in case.
Are Koi Fish Poisonous?
No, Koi fish are not poisonous.
There are some fish that secrete toxins from their scales that can harm humans and other animals, but koi aren’t one of them.
Koi fish keepers handle their pets all the time, without any worry of being poisoned by them.
Do Koi Fish Carry Diseases?
Although koi fish aren’t poisonous to the touch or innately aggressive toward humans, some may carry bacteria and parasites that could potentially harm humans.
That is why it is extremely important for koi fish keepers to know how to take proper care of their pet koi fish, and take the necessary measures to ensure that each fish stays free of disease and parasites.
Can Diseased Koi Endanger Other Koi Fish?
Even those diseases that don’t affect humans and other animals can be deadly to other koi sharing a pond with the infected fish.
For instance, Koi herpesvirus (KHV) is a virus known to inflict koi and other species of carp.
Koi herpesvirus can lead to organ failure and death within three weeks of infection.
It is said to be highly contagious; experts recommend separating the infected fish from the rest and cleaning the water in their pond immediately.
Is Koi Fish Food Harmful to Other Animals?
New koi fish keepers may wonder if koi fish food harms their other pets.
For example, what might happen if your cat or dog managed to get into your koi’s fish food? Would eating it harm them in any way? Luckily, the answer is no.
Koi fish food is made of algae and plant matter that is edible by humans and other animals, though not particularly nutritious for them.
If your pet cat or dog were to accidentally eat koi fish food, it wouldn’t harm them, but it’s also not recommended that you knowingly feed koi fish food to other animals anyway.
Can Pet Dogs and Cats Eat Koi Fish?
Some new koi fish owners may be concerned about what would happen if their pet dog or cat were to eat one of their koi fish.
First of all, it is highly recommended that if you own other pets, you should build your koi pond so that they can’t harm your koi fish in the first place.
To do so, either build a net ceiling above the bond or a raised border around it.
To answer the question at hand though; no. Eating a koi fish won’t kill your pet dog or cat.
Many koi fish keepers are able to keep both koi fish, as well as cats or dogs without incident.
Do Koi Fish Bite?
Many expert koi fish keepers recommend feeding your koi fish by hand as a way to bond with them and train them.
However, new koi fish keepers may be hesitant to do so out of fear that their koi fish might bite them.
The fact is that koi fish do nibble at their owner’s fingers, given a chance.
However, these nibbles are absolutely harmless, and most owners claim to feel a tickle when feeding their pet koi fish barely.
Do Koi Fish Have Teeth?
You might be surprised to learn that koi fish do in fact have teeth, even though they can be difficult to see.
While maintaining a full pond of your own koi fish, you may occasionally find broken koi teeth at the bottom of your pond.
If this does happen, there’s no need to panic. Koi fish teeth are known to be brittle, but they grow back very fast.
Because they have brittle teeth, koi fish are unable to use them to harm humans. However, there have been incidences where one koi fish may bite another.
Why Do Sometimes Koi Fish Bite One Another
Even if your koi fish can’t harm you, that doesn’t mean you shouldn’t be wary on the rare occasion that they do display aggressive behavior.
While attempting to mate, the male koi fish might try to bite the female.
Although they aren’t trying to kill the female koi fish, sometimes their bites can do more damage than intended.
During mating rituals, female koi fish have been known to damage their fins and even lose their scales.
If you notice a male koi being overly aggressive toward a female, you may want to separate the two, at least temporarily.
Koi fish keepers who intend to keep their koi in the same pond as other breeds of fish need to be especially careful.
As mentioned previously, koi fish are usually docile creatures.
However, given their size, they can inadvertently harm smaller fish they share space with, even unintentionally.
Most experts advise not to keep small goldfish with your larger koi fish, as the koi fish can hurt, or even kill the goldfish.
How To Prevent Koi Fish Aggression
Koi fish are known to be calm, docile creatures. It’s rare to hear of incidences where one koi may intentionally try to harm another koi or even a human, but it can happen.
Experienced koi keepers know they must take extra precautions to ensure that their koi fish cohabitate peacefully in one pond, never harming one another.
But how can a koi keeper guarantee that all their koi remain peaceful?
Provide High-Quality Water
If your koi behave aggressively toward you and their fellow pond mates, this could be a sign that the koi isn’t happy in its environment.
The first thing you need to do is measure the quality of the pond’s water, there are several metrics for doing so.
Check oxygen levels, temperatures, pH levels, and other such measures of quality, to ensure your pond is suitable for the koi living in it.
Frequently Clean the Pond
Over time, excess plant matter and food waste can collect in the water, contaminating your pond.
This can lead to some very unhappy koi fish. To avoid the displeasure of your koi, make sure to clean out your koi pond regularly.
Quarantine Aggressive Koi Fish
If only one koi fish is aggressive among several, try quarantining that particular fish until its behavior settles.
Eventually, try to reintroduce the aggressive koi back into the pond. If nothing changes, you may need to rehome that particular fish.
Provide Enough Space
Koi fish can go fairly quickly. It’s important to start with a large enough pond so that you don’t have to constantly scale up the size of the pond as your koi fish grow.
If too many koi fish are cramped together in a pond that is too small for them, it may trigger innate survival instincts, that lead your koi to fight one another for space.
Provide Plants and Shelter
It isn’t enough just to give your koi fish a large pond, you also need to provide them with plants, rocks, and other forms of shelter within their pond.
This will allow your koi to separate from one another of their own volition.
Plants allow smaller koi and other fish to hide from bigger ones, making them crucial to their survival.
Now That You Know
Now that you know so much more about the nature of koi fish, and what might lead them to behave aggressively toward their owners and other fish in their pond, what do you think?
Are you already an experienced koi keeper? If so, have any of your pet koi fish ever exhibited aggressive behavior? What do you do in such a scenario?
Or, are you interested in raising your very own pet koi fish for the first time?
Hopefully, this article helped prepare you, for the unlikely scenario that one of your pet koi fish does act aggressively toward you.
Before you start your own koi pond, it’s important to understand exactly what you’re getting into.
Raising koi is a serious commitment, and we recommend that you prepare yourself for anything that might happen so that you can give your pet koi fish a happy and healthy life.
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